[PATCH v9 4/8] KVM: Use gfn instead of hva for mmu_notifier_retry

Chao Peng
2022-10-25T15:19:41Z

Currently in mmu_notifier validate path, hva range is recorded and then
checked against in the mmu_notifier_retry_hva() of the page fault path.
However, for the to be introduced private memory, a page fault may not
have a hva associated, checking gfn(gpa) makes more sense.

For existing non private memory case, gfn is expected to continue to
work. The only downside is when aliasing multiple gfns to a single hva,
the current algorithm of checking multiple ranges could result in a much
larger range being rejected. Such aliasing should be uncommon, so the
impact is expected small.

It also fixes a bug in kvm_zap_gfn_range() which has already been using
gfn when calling kvm_mmu_invalidate_begin/end() while these functions
accept hva in current code.

Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
arch/x86/kvm/mmu/mmu.c | 2 +-
include/linux/kvm_host.h | 18 +++++++---------
virt/kvm/kvm_main.c | 45 ++++++++++++++++++++++++++--------------
3 files changed, 39 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6f81539061d6..33b1aec44fb8 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4217,7 +4217,7 @@ static bool is_page_fault_stale(struct kvm_vcpu *vcpu,
return true;

return fault->slot &&
- mmu_invalidate_retry_hva(vcpu->kvm, mmu_seq, fault->hva);
+ mmu_invalidate_retry_gfn(vcpu->kvm, mmu_seq, fault->gfn);
}

static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 739a7562a1f3..79e5cbc35fcf 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -775,8 +775,8 @@ struct kvm {
struct mmu_notifier mmu_notifier;
unsigned long mmu_invalidate_seq;
long mmu_invalidate_in_progress;
- unsigned long mmu_invalidate_range_start;
- unsigned long mmu_invalidate_range_end;
+ gfn_t mmu_invalidate_range_start;
+ gfn_t mmu_invalidate_range_end;
#endif
struct list_head devices;
u64 manual_dirty_log_protect;
@@ -1365,10 +1365,8 @@ void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc);
void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
#endif

-void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
- unsigned long end);
-void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
- unsigned long end);
+void kvm_mmu_invalidate_begin(struct kvm *kvm, gfn_t start, gfn_t end);
+void kvm_mmu_invalidate_end(struct kvm *kvm, gfn_t start, gfn_t end);

long kvm_arch_dev_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg);
@@ -1937,9 +1935,9 @@ static inline int mmu_invalidate_retry(struct kvm *kvm, unsigned long mmu_seq)
return 0;
}

-static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
+static inline int mmu_invalidate_retry_gfn(struct kvm *kvm,
unsigned long mmu_seq,
- unsigned long hva)
+ gfn_t gfn)
{
lockdep_assert_held(&kvm->mmu_lock);
/*
@@ -1949,8 +1947,8 @@ static inline int mmu_invalidate_retry_hva(struct kvm *kvm,
* positives, due to shortcuts when handing concurrent invalidations.
*/
if (unlikely(kvm->mmu_invalidate_in_progress) &&
- hva >= kvm->mmu_invalidate_range_start &&
- hva < kvm->mmu_invalidate_range_end)
+ gfn >= kvm->mmu_invalidate_range_start &&
+ gfn < kvm->mmu_invalidate_range_end)
return 1;
if (kvm->mmu_invalidate_seq != mmu_seq)
return 1;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8dace78a0278..09c9cdeb773c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -540,8 +540,7 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn,

typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);

-typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start,
- unsigned long end);
+typedef void (*on_lock_fn_t)(struct kvm *kvm, gfn_t start, gfn_t end);

typedef void (*on_unlock_fn_t)(struct kvm *kvm);

@@ -628,7 +627,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
locked = true;
KVM_MMU_LOCK(kvm);
if (!IS_KVM_NULL_FN(range->on_lock))
- range->on_lock(kvm, range->start, range->end);
+ range->on_lock(kvm, gfn_range.start,
+ gfn_range.end);
if (IS_KVM_NULL_FN(range->handler))
break;
}
@@ -715,15 +715,9 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
}

-void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
- unsigned long end)
+static inline void update_invalidate_range(struct kvm *kvm, gfn_t start,
+ gfn_t end)
{
- /*
- * The count increase must become visible at unlock time as no
- * spte can be established without taking the mmu_lock and
- * count is also read inside the mmu_lock critical section.
- */
- kvm->mmu_invalidate_in_progress++;
if (likely(kvm->mmu_invalidate_in_progress == 1)) {
kvm->mmu_invalidate_range_start = start;
kvm->mmu_invalidate_range_end = end;
@@ -744,6 +738,28 @@ void kvm_mmu_invalidate_begin(struct kvm *kvm, unsigned long start,
}
}

+static void mark_invalidate_in_progress(struct kvm *kvm, gfn_t start, gfn_t end)
+{
+ /*
+ * The count increase must become visible at unlock time as no
+ * spte can be established without taking the mmu_lock and
+ * count is also read inside the mmu_lock critical section.
+ */
+ kvm->mmu_invalidate_in_progress++;
+}
+
+static bool kvm_mmu_handle_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+ update_invalidate_range(kvm, range->start, range->end);
+ return kvm_unmap_gfn_range(kvm, range);
+}
+
+void kvm_mmu_invalidate_begin(struct kvm *kvm, gfn_t start, gfn_t end)
+{
+ mark_invalidate_in_progress(kvm, start, end);
+ update_invalidate_range(kvm, start, end);
+}
+
static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
const struct mmu_notifier_range *range)
{
@@ -752,8 +768,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
.start = range->start,
.end = range->end,
.pte = __pte(0),
- .handler = kvm_unmap_gfn_range,
- .on_lock = kvm_mmu_invalidate_begin,
+ .handler = kvm_mmu_handle_gfn_range,
+ .on_lock = mark_invalidate_in_progress,
.on_unlock = kvm_arch_guest_memory_reclaimed,
.flush_on_ret = true,
.may_block = mmu_notifier_range_blockable(range),
@@ -791,8 +807,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
return 0;
}

-void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start,
- unsigned long end)
+void kvm_mmu_invalidate_end(struct kvm *kvm, gfn_t start, gfn_t end)
{
/*
* This sequence increase will notify the kvm page fault that
--
2.25.1